The present disclosure relates to automatic background detection of a scanned document. More particularly, there is disclosed a process for identifying a background value of a scanned document that automatically discriminates signals associated with non-document areas from those of the document.
In many document processing devices, including scanners, facsimile machines, digital copiers, etc., a document or image is scanned using a device which converts the light reflected from the document into electrical charges representing the light intensity from predetermined areas (e.g., pixels) of the document. This image data, which can be in the form of digital or analog signals can be made available to an image processing system wherein the data can be further processed or modified in accordance with specific device. For example, the system may process the signals to enable transmission to a remote device for storage or reproduction, display on a CRT or similar device, reproduction by a digital copier, etc.
When processing scanned image data, it is often desirable to know the contrast of the image being scanned prior to subsequent image processing because, with this knowledge, the image processing system can process the image data so that the reproduced image has the proper contrast. Background detection processes provide one way of obtaining this contrast information. Conventional automatic background detection processes collect information relating to intensity of the scanned image and use this intensity information to determine an intensity level associated with the document background. This intensity level associated with the document background is often referred to as the “background level.”
It should be appreciated that determination of the background level of a scanned document is only as accurate as the intensity information from which it is generated. Therefore, when collecting intensity information to determine the background level of a scanned document, it is desirable to include intensity information corresponding to areas from within the document and exclude information collected form areas outside the document. Many existing methods for background detection are performed by sampling intensity information from either a sub-region of the document (typically the leading edge) or across the whole document (page). To avoid the processing and/or hardware overhead or the operator intervention associated with an a-priori determination of document size, shape and location, many of these approaches rely on a predefined measure of scanned image size, shape and location.
While these conventional approaches produce reasonable results when the predefined area accurately reflects the size, shape and location of the scanned document, the approaches may fail to accurately measure the background if the scanned document is not the same size as the predefined measure or if the scanned document is positioned such that predefined measure includes background areas other than that of the document (e.g., platen cover). For example, consider scanning a document from a platen with a white or light gray platen cover. When the document to be scanned is smaller than the predefined measure, the intensity information collected would contain intensity values corresponding to the white platen cover in addition to the intensity values of the document. If enough of the platen cover is included in the information, the background value detected would be incorrect. Therefore, it is desirable to utilize a background detection process that can discriminate intensity information obtained from non-document areas from the intensity information corresponding to the document's background when determining background levels for a scanned document. With such a process, the background value will reflect the value of the document and not the level of non document areas.